Air wire electrode for stainless steel welding

ABSTRACT

An air wire electrode comprising an outer sheath of mild steel having a central core constituting about 50 percent by weight of the electrode; the core being composed of stainless steel alloying ingredients and components of a lime-rutile-fluorspar flux system for gasless slag-shielding, the lime being present as part of a prefused lime-rutile mixture of suitable proportions, including the eutectic and stoichiometric compositions.

United States Patent 1 Sullivan Oct. 23, 1973 AIR WIRE ELECTRODE FORSTAINLESS.

STEEL WELDING [75] Inventor: Cornelius J. Sullivan, Berkeley Heights,NJ.

[73] Assignee: Airco, Inc., New Providence, NJ.

[22] Filed: Apr. 29, 1971 [21] Appl. No.: 138,790

Related US. Application Data [63] Continuation of Ser. No. 31,638, April24, 1970,

abandoned.

[52] US. CL... 219/146, 219/137 [51] Int. Cl. B23k 35/22 [58] Field ofSearch 219/137, 145, 146,

[5 6] References Cited UNITED STATES PATENTS 3,585,352 6/1971 Zvanut219/146 3,415,976 12/1968 Smith 219/146 3,177,340 4/1965 Danhier 219/1463,534,390 10/1970 Woods et a1 219/146 FOREIGN PATENTS OR APPLICATIONS1,160,069 7/1969 Great Britain 219/146 1,030,326 5/1966 Great Britain219/146 Primary Examiner-J. V. Truhe Assistant Examiner-George A.Montanye Attorney-Larry R. Cassett, Edmund W. Bopp and H.

Hume Mathews 57 ABSTRACT An air wire electrode comprising an outersheath of mild steel having a central core constituting about 50 percentby weight of the electrode; the core being composed of stainless steelalloying ingredients and components of a lime-rutile-fluorspar fluxsystem for gasless slag-shielding, the lime being present as part of aprefused lime-rutile mixture of suitable proportions, including theeutectic and stoichiometric compositions.

12 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION The advantagesof arc welding alloy steels by welding machines having means forautomatically feeding a continuous wire electrode to the welding arc arewell known. With this technique, the welding can be precisely controlledand the welding speed increased by using a flexible bare wire electrodecomposed of an outer sheath (usually of mild steel for facilitatingreduction and consolidation of the wire by drawing) with a central corecontaining alloying and fluxing materials. However, in such operationsauxiliary shielding of the arc and weld metal from the atmosphere isusually required for preventing contamination of the weld metal byoxides, nitrogen, etc. Conventional gas shielding using carbon dioxide,argon, etc., as well as slagshielding (submerged arc) are commonly usedfor this purpose.

Although various welding techniques have been proposed for using coredelectrodes without auxiliary shielding, such have in general beenlimited to the welding of mild steel. Insofar as is known, coredelectrodes for welding steels of higher alloy content have required forall practical purposes, auxiliary shielding accompanied by greater costand complexity.

For avoiding auxiliary shielding in stainless steel welding whichrequires comparatively large amounts of alloying ingredients, so-calledstick electrodes with a self-contained fluxing system have been used. Inthis instance, a mild-steel wire constituting the electrode core iscoated with a somewhat brittle composition of alloying and fluxingmaterials proportioned for supplying essential alloying chromium,nickel, etc., together with fluxing components, for shielding the weldmetal during arc deposition. However, the self-contained stick electrodeis made up in comparatively rigid, short lengths, is uneconomical, andcannot be used in automatic welding machines where continuous feeding ofthe electrode is required.

In welding operations other than for stainless steel, a so-called airwire can sometimes be used without auxiliary shielding where the steelsheath provides core volume sufficient for limited amounts of alloyingingredientsand flux components. However, for welding stainless steel ofstandard composition the required alloying amounts of chromium andnickel especially, are quite large; consequently, for usual wire sizesthe mechanical properties of the resulting thin mild-steel sheath havebeen found to be incompatible with a core of sufficient volume toaccommodate both the alloying ingredients and a complete self-containedflux system.

Attempts to combine the advantageous features of 1 the continuous barewire cored-electrode with those of the self-contained stick electrodefor stainless steel welding, have heretofore been unsuccessful, dueprimarily to the problem of making a workable cored-wire electrode ofrequired composition that is practical for continuous feed in anautomatic welding machine. This problem is further aggravated by themechanical characteristics of the steel sheath as regards wire formingand drawing; that is, if the wire sheath itself contains materialamounts of chromium and nickel the resulting composition introducesserious problems in the reduction and consolidation of the wire in thedrawing process. For this reason, air wire electrodes having an outersheath of stainless steel or the like, are not considered practical.

Hence, the invention is primarily concerned with an improved techniquewhereby a cored-electrode with mild steel sheath and self-containedfluxing system can be successfully used in automatic machines withoutany auxiliary shielding for welding stainless steel.

SUMMARY OF THE INVENTION In accordance with the invention, a cored, airwire electrode capable of use in automatic welding machines forstainless steel welding is composed of an outer sheath or tube of mildsteel and an inner central core of alloying ingredients and fluxingmaterials, the latter constituting a self-contained-fluxing system. Thecore per se is approximately equal in weight to the sheath, and for apreferred composition includes in percentage of core weight, alloyingingredients 62.80 (39.15 chromium, 18.40 nickel, ferro-alloys including3.30 manganese and 1.90 ferrosi'licon, with 0.05 pollucite for arcstabilization) and a lime-rutile-fluorspar fluxing system, 37.20, thatis characterized by compactness and gas-less slag shielding.

For achieving a compact, low volume flux system, a prefused lime-rutilemixture (that in the stoichimetric mixture constitutes calcium titanate)is used for supplying the lime content of the fluxing and slag-formingcombination. The fluxing system is comprised of 3 to 15 percent lime, 35to 83 percent rutile and 10 to percent fluorspar, and in the preferredform of the invention, the composition lies within the rutile-rich areaof the CaO-TiO -CaF ternary liquidus diagram. The fluxing systemcomponents listed above and hereinafter throughout the application, arespecified in percentage by weight of the flux fill in the electrodecore.

In practice as used in automatic welding machines, the stainless steelair wire electrodes of the invention are capable of making soundstainless steel welds without any auxiliary shielding, and withoutundercutting or excessive spatter; also, the shielding slag is easilyremoved from the weld.

A principal object of the invention therefore is an improved cored airwire electrode for welding stainless steel that can be used in automaticwelding machines for low-cost continuous welding without auxiliaryshielding.

A further object is a new self-contained fluxing system for stainlesssteel cored wire electrodes that does not require an intrusion of thewire sheath for proper fusing during the welding process.

Another and related object is an improved air wire electrode of thecharacter described above, wherein the essential alloying ingredientsfor stainless steel, together with components of a completeself-contained lime-rutile-fluorspar fluxing and slag-shielding systemare combined in the electrode core, for making up about one-half theelectrode-weight and wherein the core is sheathed by a mild steel tubemechanically suited for use of the wire electrode in conventionalautomatic welding machines.

Other objects, features and advantages will appear from the followingdescription with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view, partly in section,of the cored, air wire electrode with self-contained flux systemembodying the invention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1; and

FIG. 3 is a ternary liquidus diagram for graphically illustratingpreferred compositions of the selfcontained flux system.

DESCRIPTION OF PREFERRED EMBODIMENT The stainless steel airwireelectrode of the invention shown enlarged in FIGS. 1 and 2, is of theso-called cored-electrode type and comprises an outer sheath or tube ofmild steel and an inner, centrally disposed core or fill l2 composed ofthe essential alloying ingredients and fluxing components, the lattermaking up a complete and self-contained fluxing and slagshieldingsystem.

It is recognized that cored electrodes having a mild steel sheath arelimited as to the weight ratio between core and electrode. Where acore-fill of about 50 percent is desired, i.e. wherein the core weightapproximates the sheath weight, the sheath thickness is so reduced thatfurther reduction in thickness tends toward mechanical fabrication andhandling problems. As the total alloy contant by weight of electrodesfor stainless steels amounts to 30 percent to 35 percent, e.g., at 50percent electrode fill, the alloying ingredients in the core wouldconstitute 60 percent to 70 percent of the core by weight, it will beapparent that further addition to the core of a complete fluxing andslag shielding system necessarily involves a new approach to the problemof providing sufficient fill without excessively weakening the sheath.Using a stainless steel sheathing has been'proposed, but this isimpractical as the sheathing tends to gall during wire drawing, etc.Ordinarily acceptable flux systems and core sheathing, such as afluoride-based system tied-in for fusing purposes with a W-shaped mildsteel sheathing for welding low alloy steels, cannot be used forstainless steel welding due to the restricted fill space imposed by thesheath intrusion or similar internal partitions, etc. In the case of acored electrode having an ordinary tubular sheathing, the core or filloften contains calcium carbonate for supplyingthe lime component of aflux system. However, calcium carbonate isgas-forming under weldingconditions and tends to'decompose and expel the heated end of the corefrom the sheath. Calcium oxide per se (lime) cannot of course be used assuch in the core, due to its hygroscopic character.

It was discovered in developing the invention that calcium titanate(CaO'TiO- could be advantageously adapted for low volume use in agas-free, slag-shielding fluxing system of the lime-rutilefluorspartype. The flux system is in this instance compounded of CaO-TiO withadditional TiO as required, and CaF The calcium titanate was found to bewelladapted for use in a gasless'flux system as it is free of thedisadvantages inherent in calcium carbonate and lime as'described above,and is suitable for slag forming; it also provides a low volumecomponent that is compatible with all parts of the fill.

Ca i mflt a ats. s pf 5 2. p rsentCaQ 25 w 41 percent TiO by weightoccurs in the U.S.S.R. as a.

natural mineral, perovskite, but is not readily available as such. Anavailable commercial product is in the form of a fluffy powder that isunsuitable per se because of its poor handling qualities forthe corerequired. In a second furnace run, calcium titanate was satisfactorilyproduced with a mixture of 59 pounds rutile and 41 pounds lime (thestoichiometric calcium titanate mixture). In the wire tests listedherein, prefused mixtures including the eutectic mixture described above(which melts at 2,660F as compared with 3,560F for the stoichiometricmixture), were used in compounding the respective fluxes for the wirefill.

The flux fill according to the invention is composed of 3 to 15 percentlime, 35 to 83 percent rutile, and 10 to percent fluorspar, the prefusedmixture including all the lime and at least part of the rutile.

Fabrication of the cored wire may follow conventional practice whereinthe fluxing materials in granular or powder form are fed from a blenderonto a mild steel strip that is passed through a forming mill.Preferably, the mill shapes the sheath around the fill as a tube with anoverlapping edge for preventing flux leakage. The

tube is then drawn to the desired wire diameter, such as 0.110 inch forthe present example, with average wall thickness of 0.0108 inch. Forimproved fabrication, the strip used should have a width-to-thicknessratio of approximately 50 to l, and should be closed at a'diameterapproximately 30-percent larger than'the desired final diameter, withallowance made for an overlap of three-eighths to one-half the diameter.For making the test wires, AISI 1010 strip, 0.594 inch X 0.012 inch, wasused; no difficulty was experienced in achieving the desired core fillrange of about 49 percent to 52 percent by weight of the electrode. Withthis fill range, alloy recovery in the weld metal has been foundsufficiently good so that the alloy content may be made leaner, ifdesired, thereby providing for increased flux volume of slag formers.

For considering the composition of the fluxing system constituting partof the fill, reference is made to the CaO, TiO and CaF ternary liquidusdiagram of FIG. 3. This diagram although incomplete as to locations ofall liquidus isotherms, is however sufficiently accurate in the regionmost relevant to the invention, i.e. the area between the CaF -Tiobinary line and the CaF -TiO eutectic section, for present purposes. A

TABLE I WIRE CORE FILL Ingredient Percent in Core by Weight Manganese 3.30 Ferrosilicon 1.90 Chromium 39.15

Nickel 18.40

Pollucite 0.05 62.80 Fluorspar Flux total 37.20 Rutile Calcium titanate48% by weight Cs,0 (added for arc stabilization) For test purposes,concentrations of all alloying ingredients and pollucite were keptconstant at the total value shown, and the total flux content wasmaintained at 37.20 percent of the fill notwithstanding individualvariations in content of lime, rutile and fluorspar for respective fluxsystems.

In the first series of tests a comparatively large number of wireshaving widely different fluxing compositions, were made for studying thecharacteristics of fillet welds produced thereby; Table II is a listingof results.

The fill for the wires listed above which ranged from Thus, the fluxcompositions lying approximately within a region roughly bordered by thetest-wire points A, L, F, C and D may for practical purposes, beconsidered a preferred group having in percentage by weight of the fluxsystem, lime 7 to '14, rutile 55 to 82 and fluorspar to 40.

For further investigation and analysis of the deposited weld metal,additional wires of the A, C, F, and S flux formulations were made incontinuous lengths by a forming mill. The prefused ground eutecticmaterial previously described was used (instead of the fluffy calciumtitanate) in compounding these fluxes, and the wires in this instancewere formed from 0.594 in. X 0.012 in. A151 1010 overlapping strip asillustrated in FIG. 2. The wires were drawn to final diameter of 0.1 10in. with average wall thickness of 0.0108 in. No difficulty wasexperienced in attaining the aforesaid desired fill range of 49 to 52percent using conventional hopper feed.

TABLE IL-HO RIZONTAL FILLET WELDS Flux fill by weight M CaO T102 CaFzFillet Slag re- (percent) (percent) (percent) shape Undercut Spattermoval Soundness 8 65 37 Convex..- Slight. Light F S.

12 48 40 0....... Yes Light/moderate... F S.

12 7s 10 i r E s.

8 72 CST Slight..." Moderate F S.

4 66 do Heavy F S.

12 68 20 Light/moderate... G S.

5 60 Moderate/heavy-.. F S.

12 28 60 Moderate P S.

8 32 60 Moderate/heavy... P S.

10 50 Light/moderate S.

14 60 26 Light.. S.

8 82 10 do S.

16 74 10 Porous 19 71 10 Moderate. D0- 22 68 10 Yes... ....do 23 53 24CSP Yes-.. do. F D0.

4 36 60 Convex..- Slight. ..do.. F S.

4 76 20 N0. --do F S.

5 85 10 CSP No do F Centerline crack.

1 Slag removal good except Where locked in by undercut. Norm-E=Excellent; slumped.

48 to 55 percent) had a flux system containing the commerciallyavailable fluffy calcium titanate mentioned above. As calcium titanatein the fluffy form did not readily lend itself to even flow of the fillon the forming mill, the wires of Tables I and II were for testingpurposes floodfilled in 9 ft. lengths; also, for providing maximum fillvolume the cylindrical sheaths were butted at the edges, rather thanoverlapped as shown in FIG. 2. The overlapped edge however is preferredas it precludes flux leakage at the seam.

Reference is now made to the flux compositions of and the physicalcharacteristics of the weld deposits produced by the test wires of TableII. From inspection of FIG. 3, it will be seen that flux compositions ofthe indicated test wires located in the rutile-rich corner of theternary diagram produced the best results, i.e. wires such as C, F and Mfor example, having flux compositions in the predominately rutile area,all produced sound welds with very good bead shapes, no undercutting,easy slag removal and minimum spatter; however, wire V deep in therutile corner produced a weld with full length center-line crack. Fluxcompositions ranging further toward the lime corner, as in wires P and Qresulted in welds with gross porosity, whereas compositions toward thefluoride corner as in wires A and S for example, resulted in increasedspatter, undercut, slumping of the weld, even though the beadsthemselves were sound.

(J Good; F =Fair; P =Po0r; S =Sound; CST: Convex, slight; CSP Convex,

. l-loriz ontal single pass fillets and four-pass weld pads for analysiswere made with these wires; all wires were found to produce sounddeposits. The horizontal fillets were made at 380 to 400 amps, 33 to 37volts and 22 ipm travel speed. Weld metal analyses for the horizontalfillets are listed below in Table III, and for the pads in Table IV,with elements in both Tables listed in percent by weight of weld metal.

Table III WELD METAL ANALYSES (Fillets) Wi reFoii KISI 34 7 ba se plate(0.8 4% 65.03792 Mo, etc.)

Wires A and S on A181 321 base plate (0.44% Ti, 0.13% Mo, etc.) Wire Con AlSI 316 base plate (17.3% Cr, 12.5% No, 2.35% Mo, etc.)

' All deposits were normal except that wire C had excessive fill, thusaccounting for the comparatively high nickel and chromium contents.

posits sound. As in Table 111, wire C shows high Ni and Cr contents. dueto excessive fill.

Throughout the tests described abovefthe alloy recovery was much betterthan expected; in fact, there was no detectable loss for nickel, andloss for chro mium was very small. This is an important consideration asit provides for better utilization of the available fill space,especially where an increase in flux content or a heavier sheath asdesired, can be achieved in view of the excellent alloy recovery. Theweld metal deposited by the wires was sound in both single and multipassoperations, all conforming to AWS-ASTM chemical specifications. Theall-weld-metal impact properties at temperatures down to 320F arecomparable to published values for coated stickelectrodes and conform toASME Boiler Code requirements.

. As regards the possible extension of application of the present wireto other stainless steel alloys, Tables Ill'and IV show that the totalalloy weight content of the deposited metal is approximately between 32and 33 percent. This clearly indicates that wire of type AISI3l6'analysis, for example which typically deposits a total alloy contentof 32 percent, is within the scope of the invention; also, other wireswhich will deposit welds of alloy content comparable to the weldsdiscussed above, can readily be fabricated, as for example thoseidentified as AlSl 321 and 347. The extra low carbon grades, such astypes 308L and 316L are also feasible where strip with a maximum carboncontent of 0.05 percent is used for the sheath. Therefore, in practicingthe invention (assuming approximately 50 percent fill), the alloycontent in percentage of core weight may con- 'sist essentially of about39 to 41 chromium, 17 to 20 nickel and 3- to 7 ferroalloys.

Having set forth the invention in what is considered to be the bestembodiment thereof, it will be understood that-changes may be made inthe compositions and apparatus as above set forth without departing fromthe spirit of the invention or exceeding the scope thereof as defined inthe following claims.

1. An air wire constituting a cored electrode for arc welding stainlesssteel comprising:

a. an outer tubular sheath of mild steel,

b. the sheath having a core fill constituting by weight about one halfof the electrode and including alloying ingredients for stainless steelwelding together with components of a self-contained slag-forming fluxsystem consisting essentially of lime, rutile and fluorspar,

c. the core weight of the combined alloying ingredients bemg greaterthan the weight of the remaining core ingredients,

(1. and the flux system by itself producing during arc welding a fluxingmedium for substantially completely slag-shielding the weld metal as itis formed.

' 'air wire electrode as specified in claim 1, wherein the flux systemis composed by weight of 3 to 15 percent lime,,35 to 83 percent rutileand 10 to 60 percent fluorspar.

3. An air wire electrode as specified in claim 2, wherein the lime,rutile and fluorspar in combination make up about three-eights of thecore weight, the remainder being essentially alloying ingredients.

4. An air wire electrode as specified in claim 1, wherein calciumtitanate constitutes at least part of the combined lime-rutile contentof the flux system, and includes the entire lime component thereof.

5. An air wire electrode as specified in claim 4 wherein the calciumtitanate consists of a pre-fused mixture of lime and rutile.

6. An air wire electrode as specified in claim 5, wherein the calciumtitanate is a pre-fused eutectic mixture of lime and rutile.

7. An air wire electrode as specified in claim 5, wherein the calciumtitanate is a pre-fused stoichiometric mixture of lime and rutile.

8. An air wire electrode as specified in claim 4 wherein the calciumtitanate is perovskite.

9. An air wire electrode as specified in claim 1 wherein the alloyingingredients, in percentage of core weight, comprise 39 to'41 chromium,17 to 20 nickel and 3 to 7 ferroalloys.

10. An air wire electrode as specified in claim 9, wherein thepercentages of the alloying ingredients are about 39 percent chromium,18 /6 percent nickel, and 5 percent ferroalloys.

11. An air wire electrode as specified in claim 4 wherein the limecomponent is 7 to 14 percent, the rutile component 55 to 82 percent, andthe fluorspar component 10 to 40 percent of' the flux system by weight;

12. An air wire electrode as specified in claim 3 wherein the coreconstitutes 48 to 52 percent of the electrode weight, and the sheathconsistsof mild steel strip formed as a seamed tube with overlappingedge.

' k m 1K

2. An air wire electrode as specified in claim 1, wherein the fluxsystem is composed by weight of 3 to 15 percent lime, 35 to 83 percentrutile and 10 to 60 percent fluorspar.
 3. An air wire electrode asspecified in claim 2, wherein the lime, rutile and fluorspar incombination make up about three-eights of the core weight, the remainderbeing essentially alloying ingredients.
 4. An air wire electrode asspecified in claim 1, wherein calcium titanate constitutes at least partof the combined lime-rutile content of the flux system, and includes theentire lime component thereof.
 5. An air wire electrode as specified inclaim 4 wherein the calcium titanate consists of a pre-fused mixture oflime and rutile.
 6. An air wire electrode as specified in claim 5,wherein the calcium titanate is a pre-fused eutectic mixture of lime andrutile.
 7. An air wire electrode as specified in claim 5, wherein thecalcium titanate is a pre-fused stoichiometric mixture of lime andrutile.
 8. An air wire electrode as specified in claim 4 wherein thecalcium titanate is perovskite.
 9. An air wire electrode as specified inclaim 1 wherein the alloying ingredients, in percentage of core weight,comprise 39 to 41 chromium, 17 to 20 nickel and 3 to 7 ferroalloys. 10.An air wire electrode as specified in claim 9, wherein the percentagesof the alloying ingredients are about 39 percent chromium, 18 1/2percent nickel, and 5 percent ferroalloys.
 11. An air wire electrode asspecified in claim 4 wherein the lime component is 7 to 14 percent, therutile component 55 to 82 percent, and the fluorspar component 10 to 40percent of the flux system by weight.
 12. An air wire electrode asspecified in claim 3 wherein the core constitutes 48 to 52 percent ofthe electrode weight, and the sheath consists of mild steel strip formedas a seamed tube with overlapping edge.